91 300E Failed Smog Test by 5000% - PeachParts Mercedes-Benz Forum

JohnM. · #1 03-02-2010, 04:54 PM

Replaced the O2 this afternoon, took about an hour. First thing I noticed was that my rough idle immediately smoothed out. Can't even tell the engine is running at idle in drive, which is how it should be

. I was having some real bad random shudders at idle, so bad the first few times It happened I thought I got lightly tapped from behind!

Now the voltage readings from the O2 sensor are in the proper range, just slightly below a stoich mixture. I don't think duty cycle needs adjustment. The PO had a re-manufactured Bosch fuel distributor installed at the dealer before I got the car

...which was hellishly expensive. So AFR is something I ain't going to touch, because it's been adjusted somewhat recently. Unless it fails emissions when I take it back. But it better not, or it's owner is not going to be very happy with it.

JohnM. · #2 03-02-2010, 06:52 PM

After tooling around all afternoon running errrands there have been a lot of upgrades to the driving experience. As I stated before the idle is rock solid. Hot start is now smooth, it used to stumble for 3-5 seconds after startup.

Low end torque seems massively improved. Off the line performance is a lot better. There used to be a semi-flat spot between 1000-2500rpm in first gear. Also shifts are a ton smoother. The downshift from 2nd>1st at 25mph hooks up smooth and fast, whereas before the engine would hesitate a slight second when I kicked down and then JUMP forward somewhat violently.

Rahulio1989300E · #3 03-03-2010, 01:24 AM

Quote:

Originally Posted by JohnM.

After tooling around all afternoon running errrands there have been a lot of upgrades to the driving experience. As I stated before the idle is rock solid. Hot start is now smooth, it used to stumble for 3-5 seconds after startup.

Low end torque seems massively improved. Off the line performance is a lot better. There used to be a semi-flat spot between 1000-2500rpm in first gear. Also shifts are a ton smoother. The downshift from 2nd>1st at 25mph hooks up smooth and fast, whereas before the engine would hesitate a slight second when I kicked down and then JUMP forward somewhat violently.

This sounds very similar to what I noticed when I changed my O2 sensor about a week ago. I was suspecting that my injectors were showing their age, I had no idea that changing an oxygen sensor would make THIS much of a difference. I changed my oxygen sensor since I knew it was in the car for well beyond 60,000 miles and just wanted to replace it. My 208K mile old M103 just got a whole lot more respect in my eyes!